The present invention relates broadly to the precise registration and alignment of two or more planar work pieces with respect to each other. In particular the present invention relates to an image control board used in forming images on a lithographic plate or in contacting or duping film through multiple exposures with several individual films. The importance of having each of the individual films register identically with the image created on the plate or film by repeated exposures in the series is readily apparent.
The exposure is done in a vacuum frame. The lithographic plate and films are provided with registration holes punched from the same punch hole configuration to ensure uniformity. The lithographic plate and film are placed on the image control board in the vacuum frame with the holes receiving retractable registration pins. A glass plate covers the lithographic plate and film. A rubber diaphragm in the vacuum frame draws the film and lithographic plate on the image control board against the glass plate. In the prior art this caused the registration pin to distort the area in the film around the pin hole causing the film to buckle and go out of registration. Only a few thousandths of an inch misalignment creates an unacceptable lack of registration. One solution to this problem has been the use of spring loaded retractable pins.
Also known in the prior art are image control boards formed of a rigid material, for example, Plexiglas.RTM. acrylic plastic sheets. The conventional wisdom was that the registration pins on the board must be fixed in perfect alignment. If the fixed pins are misaligned only a few thousandths of an inch the film may buckle and registration could be lost. Because the various components of a rigid image control board are made of different materials, for example steel, stainless steel, brass, aluminum and acrylic plastic, thermal expansion is a potential problem. For example, in the case of such a rigid board with fixed pins it is possible that changes in humidity or temperature will change the fixed pin alignment in a varying degree than the individual films to be used.
The present invention solves the problems of the prior art image control board systems by, at least in part, going against conventional thought in providing registration pins that float in a multidirectional fashion within the board to maintain precise and repetitive registration of the lithographic plate and film while maintaining planarity with the glass plate.